(1) Field of the Invention:
The present invention relates to light sensitive compositions, more particularly, to compositions comprising highly sensitized polymethyl isopropenyl ketone which is a photoresist for fine pattern processing.
(2) Prior Art:
Recently, for the development of super LSI, lithography of a precision of up to submicron units attracts public attention. However, according to conventional photolithography, patterns of less than 1 .mu.m cannot be formed due to phenomena such as diffraction and interference of light, since ultraviolet rays having wave lengths of from 350 to 450 nm are used. Under the circumstances as above, techniques of electron beam exposure and soft X-ray exposure are now being developed. However, the electron beam exposure technique has disadvantages in that a large-sized computer is used and a long exposure time is required. Therefore, this technique is impractical for wafer transfer. In the soft X-ray exposure technique, there is no practical light source and mask fitting is very difficult. Further, in both techniques, devices necessitated are very large in size and extremely expensive.
If the ultraviolet rays of wave lengths of 350-450 nm employed in the conventional photolithography can be replaced with ultraviolet rays of shorter wave lengths of 100-350 nm, formation of ultrafine images or patterns of less than 1 .mu.m, is made possible, the conventional lithographic techniques can be used, and light sources such as low pressure mercury lamps, heavy hydrogen lamps and xenon-mercury lamps can be used. Therefore, this is economical and most practical for forming ultrafine images.
After intensive investigation on the techniques of forming ultrafine patterns by irradiation with ultraviolet rays of having wave lengths of from 100 to 350 nm, from this point of view, the inventors found previously that polymethyl isopropenyl ketone has a high sensitivity to ultraviolet rays of wave lengths of 100-350 nm and that a composition comprising the polymethyl isopropenyl ketone combined together with a benzophenone derivative exhibits a higher sensitivity and acts as a resist suitable for the preparation of super LSI (German Patent Application No. P.28 47 764.7 and U.S. application Ser. No. 961,120, filed Oct. 16, 1978.).
FIG. 1 shows spectral sensitivity of polymethyl isopropenyl ketone. The sensitivity range of polymethyl isopropenyl ketone is divided into two parts. Particularly, in a range of wave lengths of 210-260 nm, a high sensitivity is not necessarily shown. Consequently, it is considered that if a sensitizer which increases sensitivity in the wave length range of 210-260 nm and, further, in a wider range is found, an effective spectrum sensitization is possible from the viewpoint of wave length characteristics of xenon-mercury lamp, etc.